Attachment 4. Project Description

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ATTACHMENT 4. PROJECT DESCRIPTION

Yuba County Water Agency (YCWA) is an independent, stand-alone governmental organization created in 1959 by the YubaCounty Water Agency Actto develop and promote the beneficial use and regulation of thewater resources of Yuba County (see Figure 4-1). YCWA has a long history of actively managing the County’s water resources for beneficialuse in cooperation with its member units (districts that enter into a contract with YCWA for the delivery of water or repayment of infrastructure to deliver water), stakeholders, and local, State of California (State), and federal agencies. An example of this successful management is YCWA’scontribution to reversing a potentially serious overdraft situation in the South Yuba Groundwater Subbasin. Figure 4-2, a representative hydrograph of groundwater elevations in the South Yuba Groundwater Subbasin, shows that water levels declined an estimated 130 feet between 1948 and 1981. In 1984, YCWA began delivering surface water from its New BullardsBar Reservoir to the subbasin to offset groundwater extraction, resulting in a groundwaterelevation rise to near-historical levels.

After recovery of groundwater storage and levels, YCWA took an active role in responsibly managing and utilizing the groundwater resources of Yuba County for the benefit of water users in the County and throughout the State. As an example of this management and utilization, YCWA coordinated groundwater substitution transfers in 1991,1994, 2001, 2002, 2008, 2009, and 2010. Groundwater substitution transfers occur when water users forego their allocated surface water supplies and instead pump groundwater, allowing the surface water to be used downstream. As described below in greater detail, increased understanding of the groundwater system in Yuba County is critical to the continued, long-term success of the management program.

4.1Proposed Project

4.1.1Project

YCWA proposes development of a numerical groundwater model that can be used to make well-informed decisions about groundwater management in Yuba County. Tasks to be performed for this Project include:

  1. Reviewing and summarizing existing groundwater modeling codes and studies. Based on the review, selecting a modeling code that is well suited to meeting the objectives of this Project.
  2. Updating the existing hydrogeologic conceptual model for the groundwater basins in Yuba County.
  3. Developing input datasets for the selected model.
  4. Running and calibrating the groundwater model.
  5. Documenting the model development process, all input data sets, adequacy of model calibration, and limitations and suggestions for future use.
  6. Managing the Project management to ensure it is completed on time, on budget, and consistent with high standards of quality.

YCWA will ensure technical feasibility of the Project by selecting a widely used and accepted modeling code in Task 1, and by following established methodologies used in similar modeling studies in California during the data compilation and model calibration tasks.

Figure 4-1. Yuba County Water Agency Service Area and
Groundwater Subbasin Locations

Figure 4-2. Groundwater Elevation Hydrograph for a Well in Brophy Water District

4.1.2Goals

YCWA developed and adopted a Groundwater Management Plan(GWMP) in 2005, and adopted an updated GWMP in 2010. The complete GWMP is included as Attachment 3d of this grant application. The goal of the YCWA GWMP is to:

“…maintain a viable groundwater resource for the beneficial use of the people of Yuba County.”

Basin Management Objectives (BMO) described in the GWMP include:

  • Maintaining groundwater elevations that provide for sustainable use of the basin
  • Protecting against inelastic land subsidence
  • Maintaining and improving groundwater quality
  • Protecting against adverse impacts to surface water flows
  • Improving the understanding of groundwater in Yuba County

YCWA’s goal for the Project, which is consistent with the GWMP goal, is to develop a numerical model that supports groundwater resource management for the benefit of the people of Yuba County. Objectives for the groundwater modeling Project are consistent with the BMOs from the GWMP, and include:

  • Enhanced ability to evaluate groundwater management scenarios, including groundwater substitution transfers, to understand the potential for changes in groundwater levels and storage, and to prevent overdraft of the aquifer
  • Increased understanding of the locations and quantities of recharge to the aquifer and the ability toidentify recharge areas that need to be protected

A calibrated numerical model can satisfy both the above objectives. For example, as YCWA and its member units plan for groundwater pumping during a given year, a numerical model can be used to predict the distribution of resultant groundwater levels in space and time. The results can be used to optimize the distribution and timing of pumping to maximize benefits and minimize the risk for third-party impacts. Quantification of the groundwater recharge components (e.g., infiltration of precipitation, recharge from streams) will allow for a designation of important recharge areas that must be protected, and will help satisfy the requirements of Assembly Bill (AB) 359. AB 359 requires agencies to include maps of groundwater recharge areas in their GWMPs.

Secondary goals for the project are listed below. These are listed as secondary goals because they (1) are within the long-term groundwater management goals for YCWA, and (2) can be addressed to a limited degree by the proposed Project. However, to be completely addressed these secondary goals may require additional studies (e.g., collection of field data) that are beyond the scope of the Project. Section 4.5 of this attachment discusses ongoing use of the model and how some of the secondary goals could be more completely addressed. The secondary goals are as follows:

  • Evaluate groundwater management scenarios to prevent subsidence of land surface
  • Better understand interactions of surface water and groundwater, including groundwater recharge at the Yuba Goldfields
  • Better understand how changing land use (e.g., agriculture to residential) in Yuba County could impact groundwater resources

4.1.3Study Area

The study area for this Project will include, at a minimum, the groundwater subbasins beneath Yuba County, consisting of the portion of the North Yuba Groundwater Subbasin (California Department of Water Resources [DWR]Basin 5-21.60) within Yuba County and the entire South Yuba Groundwater Subbasin (DWR Basin 5-21.61). Both subbasins are part of the larger Sacramento River Groundwater Basin (DWR Basin 5-21). Adjacent groundwater subbasins will be included in the model as necessary to develop a technically sound groundwater model.

No facilities will be constructed for this study.

4.2Collaboration with Other Agencies

4.2.1Historical Collaboration Efforts

YCWA worked within a broad coalition of 17agricultural, environmental, and fisheries interests, including State and federal agencies, todevelop an innovative set of agreements that together form a framework – the Lower YubaRiver Accord (Yuba Accord) – that resolved nearly 15 years of controversy and litigationover instream flow requirements for the lower Yuba River. The Yuba Accord contains three agreements:

  1. Fisheries Agreement: Establisheshigher minimum instream flows during specified periods of the year and a monitoring and evaluation program for the Lower Yuba River and its fisheries
  1. Conjunctive Use Agreements: Implementsa comprehensive conjunctive use program, locally managed with irrigation districts in Yuba County, to responsibly integrate the use of surface water and groundwater supplies and improve water supply reliability
  2. Water Purchase Agreement (WPA): Providesa long-term water supply for fish and wildlife in the Sacramento-San Joaquin Delta (Delta) ecosystem and supplemental water supplies for California cities and farms through a long-term purchase agreement with the DWR. Exhibit 3 of the WPA, Groundwater Monitoring and Reporting Program, describes the types and frequency of data that will be collected by YCWA, DWR, and the Accord member units; the process that will be used to determine pumping volumes; and the process for YCWA and the Member Units to deal with third-party impacts.

The Yuba Accord was successfully implemented in 2008. In 2008, 2009, and 2010, member units pumped 48,875, 88,900, and 66,213 acre-feet of groundwater, respectively, for groundwater substitution transfers. These transfers resulted in a direct financial benefit to Yuba County and a benefit of increased water supply reliability to water users downstream who had purchased the water.

In addition to collaboration related to the Yuba Accord, YCWA also involved the public and other agencies during development of the GWMP. YCWA hosted public meetings during GWMP development and invited participation from 22 agencies within and adjacent to Yuba County, including member units, other irrigators who rely on groundwater, public water suppliers, Beale Air Force Base, and water agencies in adjacent counties. Public noticing was performed in the local newspaper and on the YCWA website before public meetings and before adoption of the GWMP by the YCWA Board of Directors.

4.2.2Collaboration for the Proposed Project

YCWA expects that collaboration with other agencies and stakeholders will improve the successful implementation of the Project. During Project development, it is foreseeable that collaboration would occur with groundwater modeling developers at DWR or the U.S. Geological Survey (USGS). Both of these agencies maintain groundwater modeling codes that are widely used in California, and one of the first tasks under the proposed work plan is to determine which code to use for the YCWA model. Both DWR and USGS have expressed a general willingness (e.g., at public meetings and workshops) to help local agencies implement their models. The degree to which those agencies are involved depends on which model is selected for the Project, and to what degree the modeling direction chosen for the Project relies on data from the existing regional models those agencies maintain.

YCWA also plans to present information and solicit feedback on the study from their member units. As described below in Section 4.6, YCWA and the member units collaborate each spring to plan for groundwater substitution transfers. YCWA expects to use the groundwater model each year when planning for the amount and timing of groundwater pumping for transfers.

YCWA will share information about the model development at a public meeting, for which stakeholders involved in development of the GWMP will be invited. One particular stakeholder group that may be interested in development of the model is Yuba County. YCWA provided extensive comments to Yuba County for the last Yuba County General Plan Update, which was adopted in 2011. The General Plan includes a series of objectives related to water resources, including protection of groundwater recharge areas and preventing overdraft of groundwater.

Documentation (e.g., reports, technical memoranda, meeting minutes) developed for the Project will be posted to the YCWA website. YCWA identified the need to create a public document sharing capability in the 2010 GWMP, and expects to have a solution in place by the end of Calendar Year 2012, likely using a Microsoft SharePoint platform.

4.3Project Need

A groundwater model would be an important addition to YCWA’s“tool box” for analyzing groundwater conditions in Yuba County. Development of a groundwater model was identified as a direct management action in the GWMP under the component category associated with groundwater sustainability. The GWMP states that increased understanding of how groundwater responds to various stressors (e.g., pumping, changes in aquifer recharge, and changes in climate) is critical to ensuring the long-term sustainability of the resource.

One area where additional, robust analysis tools will be crucial is planning for future groundwater substitution transfers. Requirements for groundwater substitution transfer planning under the Yuba Accord, as stated in the WPA, require YCWA to determine “the amount of water that can be pumped within the safe yield of the basin without contributing to long-term overdraft and without resulting in significant unmitigated impacts to other groundwater users in the basin.” The WPA specifies that suchdetermination will be made in the spring of the year during which groundwater substitution transfers are planned.

In an attempt to meet the above requirements, YCWA developed the Groundwater Adaptive Management Tool (GAMT) in 2008. The GAMT includes a set of response and recovery functions for each analysis unit (e.g., each member unit or hydrologic unit) that were developed as statistical relationships between historical pumping, precipitation, and water levels in dedicated monitoring wells distributed throughout the basin. The response and recovery functions are used to predict water-level response (i.e., drawdown and recovery) to pumping volumes in the analysis unit.

While the GAMT has been successfully applied for groundwater management planning, it has several limitations. First, the GAMT generates a predicted response for the entire analysis unit. For example, the response and recovery functions may predict a drawdown of 15 feet in response toa given member unit’s planned pumping. However, the prediction does not account for spatial variations in drawdownwithin a member unit. Second, each response and recovery function does not explicitly consider the effects of pumping or other stressors outside of the analysis unit. In other words, the predicted drawdown in response to pumping does not consider pumping from adjacent, and often hydraulically connected, analysis units. A three-dimensional groundwater model is wellsuited to the purpose of supporting groundwater management analysis, and would represent a significant improvement on the existing GAMT.

4.4Project Benefits

The proposed Project will yield substantial benefits to groundwater management in Yuba County. Those benefits include:

  • IncreasedWater Supply Reliability –A calibrated groundwater model will lead to better-informed groundwater management decisions, which would help ensure the long-term health of the basin in terms of water levels, storage, and maintenance of water quality. This will benefit agricultural and municipal groundwater users within the County in the form of increased water supply reliability. Additional benefit is realized by others outside the County through their participation in groundwater substitution transfers, which increase water supply reliability for downstream water users throughout the State.
  • Identification, and Subsequent Protection, of Recharge Areas – As noted in Section 4.1, one output of a calibrated groundwater model is a quantification of the recharge components (e.g., infiltration of precipitation, recharge from streams). Recharge from the model can be compared with other water budget estimations (e.g., from the 2008 Hydrogeologic Understanding of the Yuba Basin report [YCWA, 2008]), and can be used to identify areas of high recharge. AB 359 requires that agencies include maps of such areas for a GWMP, and those areas can subsequently be protected to maintain their recharge flows and prevent potential aquifer contamination.
  • Manage Third-Party Impacts – A calibrated model can be used as a tool to prevent, verify, manage, and resolve third-party impacts. During planning for groundwater management scenarios, YCWA can evaluate how different actions (e.g., pumping volumes) result in changes to water levels outside of the member units. YCWA can then implement those management scenarios where the potential to result in impacts is minimized. If a potential third-party impact is reported, YCWA can use the model to (1) verify that the impact is a result of pumping by one, or more, of the member units,and (2) determine how best to resolve the impact (e.g., how deep to lower the pump in the impacted well).
  • Increased Understanding of Groundwater Resources – During construction and application of numerical groundwater models, scientists and engineers can easily test hypotheses from the conceptual model development phase. Therefore, results from the conceptual model and numerical model feed back into each other and both are improved. As project engineers use the model to plan for a groundwater substitution transfer, for example, they may have an idea from their own conceptualization of the system regarding the amount of pumping a portion of the basin can sustain. The groundwater model can be used to either verify, or potentially refute, their conceptualization, and the result is an increased understanding of how the groundwater system “works.”Increased understanding of groundwater resources is a BMO from the GWMP.
  • Identification of Data Gaps – Through model verification and calibration, the Project team will identify areas where the model is either not well calibrated, or data to calibrate to does not exist. This effort can drive future studies in the basin to collect groundwater-related data.

4.5Ongoing Use

YCWA will use the groundwater model at least as often as any year during which a groundwater substitution transfer is planned. Using the groundwater model to evaluate potential changes in storage for different pumping scenarios can be incorporated into the routine planning process for groundwater substitution transfers. As it supports YCWA operations, additional processes may be included in future modeling. Funding for the continued ongoing use will be provided from revenues from water transfers and power generation.

Future updates could address some of the secondary goals identified in Section 4.1, which include understanding land subsidence, groundwater surface water interactions, and how future land-use change could impact groundwater resources. Land subsidence is generally of lesser concern in Yuba County and in the Sacramento Valley relative to the San Joaquin Valley. Land subsidence data (e.g., from an extensometer) are likely not available in Yuba County, which would make calibration for this parameter difficult. Management scenarios simulated by the model can be evaluated in terms of preventing future land subsidence by selecting scenarios that prevent drawdown of groundwater levels below historical lows.

Groundwater/surface water interactionswill be addressed for the Project in the sense that the selected model will likely include a stream simulation package. However, stream/aquifer interactions are highly variable spatially and temporally, and accounting for these interactions at a high degree of confidence may require additional field studies that are not within the scope of the Project. YCWA may opt to perform those studies in certain areas (e.g., the Yuba Goldfields) at a later date and those future studies could support the simulation of groundwater/surface water interactions.

Yuba County Water Agency4-1July 2012

Local Groundwater Assistance Grant Application